Edge Mobility is known as a technique that provides mobility with IP layer, with which, even if a link connected to a node is changed one after another in the Internet as the node moves, communications with a communication partner node can be continued (see Non-patent Document 1, for example).
According to the Edge Mobility, as shown in FIG. 1, defined are: a core network 5, which is a network to which mobile nodes 1, 3 are connected; access gateways (MAG: Mobile Access Gateway) 7, 11 serving as default routers for the mobile nodes 1, 3; and location management device (LMA: Local Mobility Anchor) 15 that manages MAGs 7, 11 with which the mobile nodes 1, 3 are associated.
Using the MAGs 7, 11 to which the mobile nodes 1, 3 are connected as location information of the mobile nodes 1, 3, the LMA 15 manages a correspondence between identification information of the mobile nodes and that of the MAGs (15a). As the mobile nodes 1, 3 move, the LMA 15 maintains the location information by constantly updating the MAGs 7, 11 to which the mobile nodes 1, 3 are connected.
The mobile nodes 1, 3 hold unique IP addresses for identifying themselves, and specify the IP addresses as a transmission destination and a transmission source of transmission/reception packets between the mobile nodes 1, 3. Then, the mobile nodes 1, 3 transmit the packets to the core network 5. The MAGs 7, 11, which serve as connection points to the mobile nodes 1, 3 in the core network 5 transfer the packets to the LMA 15. From the location information 15a, the LMA 15 acquires the MAG (e.g., the MAG 11) with which the mobile node as the transmission destination (e.g., the mobile node 3) is associated, and transfers the corresponding packet to the MAG.
Thus, within the core network 5, the packet between the mobile nodes 1, 3 is delivered through packet transfer by the MAGs and the LMA.
A specific example of the packet delivery will be described with reference to FIG. 1 and FIG. 2.
For example, the mobile node (1)1 transmits a packet addressed to the mobile node (2)3 (FIG. 2(a)). The transmission source of the packet has the IP address of the mobile node (1)1, and the address of the transmission destination is the IP address of the mobile node (2).
The transmitted packet is received by the MAG (1)7, which is a default router for the mobile node (1)1. The MAG (1)7 transfers the packet to the LMA 15 in the core network 5. A unit for the transfer may be achieved, for example, by a transfer using packet encapsulation by the MAGs and the LMA (see FIG. 2(b)), tunneling using GRE tunneling (see Non-patent Document 2), or label switching using MPLS (see Non-patent Document 3).
The LMA 15 acquires the MAG (2)11 from the location information of the mobile node (2)3, which is the destination of the transferred packet, and transfers the packet to the MAG (2)11 (FIG. 2(c)).
Since the MAG (2)11 is associated with the mobile node (2)3, that is, the destination of the transferred packet, the MAG (2)11 delivers the packet to the mobile node (2) (FIG. 2(d)). Thus, the packet from the mobile node (1)1 to the mobile node (2)3 is delivered through a transfer based on the location information managed by the MAGs and the LMA within the core network 5. A packet from the mobile node (2)3 to the mobile node (1)1 is delivered by following the above-mentioned steps in reverse order (FIG. 2(e)-2(h)) while the transmission source and the transmission destination in the IP header of the packet are swapped.
In the Edge Mobility, the above-mentioned method allows each mobile node to continue communications only by changing the MAG which is the default router with the movement of the mobile node. Within the core network, communications between the mobile nodes is achieved by updating the location information and performing packet transfer at the LMA and the MAGs. Thereby, the Edge Mobility has an advantage that movement process performed by the mobile nodes is minimized, and the number of control signals in wireless communication area is reduced.    Non-patent Document 1: H. Levkowetz, Ed, et al., “draft-giaretta-netlmm-dt-protocol-01” NetLMM WG Internet-Draft Sep. 18, 2006    Non-patent Document 2: Farinacci, D. et al., “Generic Routing Encapsulation(GRE)”, RFC 2784, March 2000.    Non-patent Document 3: Rosen, E., et al., “Multiprotocol Label Switching Architecture”, RFC 3031, January 2001.    Non-patent Document 4: 3GPP TS 23.003V5.2.0, “Numbering, addressing and identification(Release 6),” March, 2004.